Stroke is a disruption of blood to a portion of the brain. The two main mechanisms are occlusion of a blood vessel (ischemic stroke) or hemorrhage of a blood vessel (hemorrhagic stroke). Ischemic stroke is significantly more common. Current state of the art treatment for ischemic stroke includes the injection of tissue plasminogen activator (tPA) within four hours of the event. Some evidence also points to a benefit from tPA out to 12 hours. Alternate therapies include mechanical dislocation or retrieval of the clot. These treatments are effective because the brain has significant collateral blood flow. Thus, when the primary blood supply to an area is disrupted, collateral flow provides some amount of oxygen to the affected tissue. The quantity is dependent on the size of the vessel obstructed, the location of the obstruction, blood oxygen level, and cerebral blood flow volume. The model for this situation is an area of dead tissue (infarction) that is dead and unrecoverable. Surrounding this tissue is the penumbra; a zone of oxygen depleted tissue. This tissue ranges from dying tissue through tissue experiencing insignificant oxygen level drops. Clearly within this continuum there exists tissue that is not dead but is not functioning due to oxygen deficit. Stroke intervention is thus intended to recover as much of the penumbra as possible, limiting the amount of tissue killed in the brain.
One solution to increasing the effectiveness of treatment is to increase the amount of oxygen delivered via collateral blood flow. Unlike some parts of the body, increasing blood pressure does not generally increase flow to the brain. A solution proposed in U.S. Pat. No. 6,743,196, to Barbut et al., is to insert a balloon into the aorta to partially occlude the aorta above the renal arteries as a means of increasing cerebral blood flow. Limitations of this device and method include mechanical complexity, constant monitoring requirements, and maintaining arterial access for the length of its use. Additionally, an inherent drawback with using a balloon to occlude a vessel is that balloons are always susceptible to failure (e.g., popping, leaking).
A device that is to be placed in an artery must address additional concerns compared to devices placed in veins because of the hemodynamic differences between arteries and veins. Arteries are much more flexible and elastic than veins and, in the arteries, blood flow is pulsatile with large pressure variations between systolic and diastolic flow. These pressure variations cause the artery walls to expand and contract. Blood flow rates in the arteries vary from about 1 L/min to about 5 L/min.
A need exists for a less complex, easily delivered, temporary arterial occlusion device that partially occludes an artery to increase cerebral blood flow, while avoiding the drawbacks of the prior devices. An associated filter that captures embolic material would be advantageous as well.